The main goal of the proposed experiments in this Exploratory/Developmental R21 application is to determine whether pituitary adenylate cyclase-activating polypeptide (PACAP) in the brain may mediate stress-induced behavioral manifestations. During the past decade since the discovery of PACAP, much has been learned about the molecular biology, cellular action and distribution of PACAP, but behavioral characterization of this potentially important peptide is still lacking. PACAP has a widespread, yet unique distribution in the brain with the highest concentrations observed in the hypothalamus, extended amygdala and lower brainstem, regions that are highly relevant for the processing of neuroendocrine and behavioral manifestations of stress. Based on preliminary evidence from our work and others we hypothesize that the central actions of PACAP participate in the elaboration of the stress response and that PACAP may act to potentiate naturally-occurring stress-induced behaviors. Within the time limit of the proposal, we plan to explore the behavioral role of PACAP specifically in the hypothalamic paraventricular nucleus (PVN) and the central nucleus of the amygdala (CeA). Aim 1 will investigate the dose-response and brain site-specificity of post-stress behavioral events following restraint stress and open field exposure or the tactile startle reflex following local microinjections of PACAP into the PVN or CeA. Aim 2 will focus on the possible role of endogenous PACAP at the level of the PVN and amygdala and will use local microinjections of a selective PACAP receptor antagonist. Differential blunting of stress-induced behaviors - based on the location of the injection site and the type of behavioral parameter - will be used to determine the site specific role of endogenously released PACAP in stress activation. It is anticipated that data from these experiments will provide novel information regarding some of the salient brain sites for the central actions of PACAP, which will be applicable toward a better understanding of stress-related disorders.